1. Field of the Invention
The present invention relates generally to a method and a hand tool for plaster spreading and more specifically to serrated hand tools for spreading plaster and the like. In particular, the hand tool of the invention can be effectively utilized for spreading a plaster or a joint compound over a taped surface joint such as between two sections of a drywall.
2. Description of the Prior Art
Construction practice have long required a reliable method and appropriate hand tool to spread plaster and other similar type compounds such as gypsum, cement, mortar, grout, joint mixes, spackling pastes, etc. All of these and other similar compounds are described herein as xe2x80x9cplasterxe2x80x9d for the purposes of this specification.
For an experienced worker, spreading a plaster compound over a perfectly flat and well prepared surface does not present a challenge. It is when the surface is not flat as is encountered in most cases, when the presently known spreading methods need improvements.
In a commonly known plaster spreading technique, a hand tool or trowel with a straight edge is used to take some soft plaster from a container and apply it over the working surface trying to maintain a constant thickness of the layer of plaster. This thickness depends on the skill of the worker and the force with which the plaster is applied. However, when the surface has bumps or valleys, maintaining the constant depth becomes quite difficult. As a result, the final surface of the hardened compound is not perfectly flat. In order to improve this technique, it is known to apply the plaster in several steps, building up the plaster layers in a gradual way. This method requires a long time to complete because every consecutive layer of plaster has to cure at least 1 to 2 hours before the next one can be applied. Typically, at least three layers of plaster are applied this way to achieve a good result. Care should also be taken not to allow cracking of the plaster compound which may occur due to excessive and uneven thickness of the plaster layer. In addition, due to natural irregularities of this plaster application method, some hardened plaster has to be periodically removed to smooth out the surface which requires more working time. Finally, that and excessive thickness of plaster also lead to a higher consumption of plaster material and hence, higher material waste.
Plaster spreading over a taped surface joint presents a separate challenge. Using a commonly known plaster spreader with a blade having a straight edge, a construction worker has to go through the following four steps:
1. A narrow spreader is used first to place a thin layer of joint compound over a drywall surface joint so a paper (for example SHEET ROCK JOINT TAPE 2116 INxc3x97250 FT ROLL) or a plastic (for example FIBA TAPE 295S) joint tape can be placed over it to cover the area of the joint and prevent it from future separation;
2. After allowing the joint to dry, a wide spreader is used to place two thin layers of plaster over the joint area with enough time in between the coats to allow the first wide coat to dry;
3. Again allowing the two thin layers to dry completely, a sanding procedure is conducted to smooth the surface; and finally
4. The final plaster layer is then placed over the area to bring the surface up to its finished geometry.
Depending on the temperature and humidity in the room, the time needed for drying of each of the layers may vary but generally it stays in the range of between 5 to 6 hours. This process requires a lot of time, as well as a construction worker with very high level of skills to achieve a good result. A method and a device therefore are needed to reduce the total time for making the joint and to reduce the skill level of a construction worker without sacrificing the quality of the end result.
Serrated or notched trowels and hand tools are known in the prior art mostly for applying glue and tile compounds. They typically have a plurality of V-shaped or square notches along the working edge and are designed to evenly distribute the paste preparing the surface to be covered with tiles, linoleum and alike. Following examples illustrate some known serrated hand tools.
U.S. Pat. No. 2,287,231 by Cathcard is directed to a paste spreader for spreading paste, cement, glue and the like on a surface to be covered with a covering such as linoleum which evenly distributes the paste. The spreader blade is fabricated of a flexible material and is serrated along one edge.
U.S. Pat. No. 2,824,330 by Williams is directed to a spreader for cement and the like on a surface to be covered with a covering, such as Formica, which evenly spreads the cement. The spreader blade is square and is removably attached to a handle. Each of the four edges of the blade has different sized notches or serrations.
U.S. Pat. No. 3,916,472 by Carder is directed to a trowel for applying adhesives to a surface such as a floor or wall to be covered. The edges of the trowel are serrated to evenly spread the adhesive.
U.S. Pat. No. 4,316,302 by Clark is directed to an adhesive spreading trowel having all four edges either straight or serrated and is adapted for manufacture by injection molding.
U.S. Pat. No. 4,654,919 by Lieberman is directed to a spreader for applying plaster and cement to wallboard. The spreader has a spreader blade attached to a handle with a backing layer next to the blade to add rigidity to the blade. The edge of the blade extends past the edge of the backing layer. The plate is made of a flexible material such as plastic and has a straight edge as opposed to a serrated edge.
U.S. Pat. No. 4,804,321 by Riesgo is directed to a cement spreader with a blade having a plurality of squared notches.
U.S. Pat. No. 5,231,729 by Rose is directed to a tilers trowel having square notches and adjustment means for limiting the depth-of material which can be applied.
U.S. Pat. No. 5,524,316 by Johnson is directed to a hand tool for spreading plaster on a substrate such as a ceiling and alike in decorative patterns. The tool has stiff but resilient serrated blade and a handle attached to the blade at an opposite or proximal edge from a serrated distal edge. Tool alignment marks are also provided to aid in decorative application of the plaster compound.
Finally, U.S. Pat. No. 5,778,482 by Sbrigato is directed to a serrated spreader for a cold-coat of roofing tar. It contains a hard rubber blade with serrations, which, when pushed over the surface to be roofed, spreads the desired coat of tar over a predetermined width of the surface to be roofed.
These and other known devices of the prior art fail to address the main problem of the plaster spreading work, namely allow for a quick to apply method of accurate plaster spreading over an imperfect surface without the need for multiple repetitive applications of plaster. Therefore, the need exists for a method and a hand tool to allow for such improvement in the plaster application technique and especially over a joint surface. In addition, the need exists for a plaster application method and a hand tool allowing for lower level of skill required to achieve smooth final surface, reducing the drying time between the layers, reducing the tendency of plaster to form cracks, and reducing the plaster material waste.
Accordingly, it is an object of the present invention to overcome these and other drawbacks of the prior art by providing a novel method and a hand tool for plaster spreading using a serrated edge principle.
It is another object of the present invention to provide a method and a hand tool for plaster spreading allowing to substantially reduce the total time required to achieve the final smooth surface joint.
It is a further object of the present invention to provide a method and a hand tool for plaster spreading allowing to achieve a final smooth surface over somewhat irregular initial surface, all with lower level of worker skills.
Finally, it is another object of the invention to provide a method and a hand tool allowing plaster spreading with minimum waste of plaster material.
The basics of the serrated edge design and its use for plaster application were described in detail in the previous co-pending patent application. According to the method of the instant invention, a commonly known serrated edge principle is used in a novel way to aid in plaster spreading over a joint surface. After the surface of a joint is initially prepared to eliminate larger defects, the first, third and fourth steps of a novel method are the same as was described above. It is the second step and the use of a novel tool which is different and allows for the above mentioned objectives.
The tool of the present invention has a flexible metal blade equipped with a handle. The blade edge has three sections: the first and the third side sections are equipped with serrated teeth in a similar way as was described in the previous patent application. The second or central section has a cutout which is designed to allow a thicker layer of plaster to be placed over a tape of a surface joint.
According to a method of the invention, the second step in the operation of applying plaster is done using a hand tool of the invention in such a way that in one step a thicker layer of plaster is placed over the tape, while two thin serrated layers of plaster are placed on both sides of the tape. Once dry, only the finishing layer of plaster needs to be applied on top of the layer placed in the second step.
For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be made to the accompanying drawings and descriptive matter in which there is illustrated a preferred embodiment of the present invention.